The present invention relates to a folded cavity laser; and, more particularly, to a folded cavity surface emitting laser by employing an astigmatic microlens which can correct the asymmetric beam shape due to the asymmetric of active medium.
With popularization of Internet, a speedy optical communication network is actively under-construction and with increasing demands, the optical communication network spreads from a backbone network to an individual user. Now, cost competitiveness of a photo device is being a big barrier in populating the optical communication.
A conventional edge-emitting laser can be easily manufactured, however, since a cavity of the conventional edge emitting laser is formed by cleaving its function must be measured after a packaging. Moreover, the conventional edge emitting laser has an astigmatism, meaning, a shape of an emitting beam has distorted by an asymmetry of a laser active medium, along to a horizontal and a vertical direction in an epitaxial layer. The distorted beam shape makes a mode coupling efficiency deteriorate and increases a packaging cost.
A surface-emitting laser is a kind of laser devices, which complements the above problems, and has two types, i.e., a folded cavity type and a vertical cavity type.
The folded cavity type makes 45xc2x0 reflecting mirrors by using an ion etching and a chemical wet etching, instead of a cleaved facet, wherein the 45xc2x0 reflecting mirrors emit a light beam to the epitaxial layer, vertically, thereby measuring an element characteristics in a state of wafer. However, the asymmetrical radiation angle problem is not solved still.
In the vertical cavity type, a distributed Bragg reflector (hereinafter, referred to as a DBR) is grown top and bottom of the active medium, through epitaxial growth, so that an oscillation direction is being vertical on the epitaxial surface. Therefore, the vertical cavity type controls its beam shape to have a circular symmetry.
Recently, an 850 nm vertical cavity surface emitting laser device has been developed.
Actually, the progress of vertical-cavity surface-emitting laser development in 1.3 xcexcm to 1.5 xcexcm, which can be used over 300xcx9c500 m, is slow. It is because, materials which are used in a long-wavelength laser have inferior thermal characteristics and the vertical cavity surface emitting laser requires a strict optical gain condition.
Especially, in a 1.3 xcexcm wave length, InGaAsN and InGaAsP materials are realized as an edge emitting laser device in GaAs and InP substrates, however, the vertical cavity surface emitting laser device using this material has not been reported yet and it shows manufacturing difficulties of the above-mentioned device.
It is, therefore, an object of the present invention to provide a folded cavity laser which complements a radiation difference that is caused by an asymmetry of a laser mode, by integrating an astigmatic microlens with the laser device.
Another object of the present invention is to present a folded cavity laser appropriate for mass production through a semiconductor manufacturing process without extra beam alignments, and provide a folded cavity laser which has improved characteristics comparable to those of the vertical-cavity surface-emitting laser.
In accordance with an aspect of the present invention, there is provided a folded cavity laser for generating a laser beam, comprising: a substrate provided with a distributed Bragg reflector (DBR); an active medium formed above the DBR for amplifying the laser beam; a first and a second mirrors formed on sides of the active medium, respectively, for making a horizontal cavity and for reflecting the amplified laser beam to the DBR; and a microlens, formed on the substrate opposite the DBR, for making the amplified laser beam astigmatic after passing therethrough.
In accordance with another aspect of the present invention, there is provided a folded cavity laser incorporating therein a microlens which is in the form of cylinder.
In accordance with another aspect of the present invention, there is provided a folded cavity laser incorporating therein a microlens which is a polymer pattern, formed by a photolithography process.
In accordance with another aspect of the present invention, there is provided a folded cavity laser incorporating therein mirrors which are inclined approximately 45xc2x0 with respect to an optical axis of a horizontal cavity.
In accordance with another aspect of the present invention, there is provided a folded cavity laser incorporating therein a laser active medium which is InGaAsN material and a substrate which is GaAs material.
In accordance with another aspect of the present invention, there is provided a folded cavity laser incorporating therein an active medium which is any one selected from a group consisting of InGaAsP, AlInGaAs or InAs quantum dot, and a substrate which is InP material.
In accordance with another aspect of the present invention, there is provided a folded cavity laser incorporating therein a microlens which is a GaAs pattern formed by patterning and etching a substrate.